1. Field of the Invention
This specification generally describes a method and an apparatus for forming images, and more particularly describes a so-called tandem method and an apparatus capable of forming images with reduced color registration errors.
2. Description of the Related Art
There is a background color image forming method and apparatus of a type often referred to as a tandem image forming method and apparatus.
The tandem image forming apparatus has a plurality of photoconductive members disposed therein in parallel, each of which corresponds to one of color components that form a target image data. The image forming apparatus further includes an optical writing device, an image forming device, and a traveling member. The traveling member may be either a conveyor member that conveys a transfer sheet thereon or an intermediate transfer member.
The optical writing device optically writes a latent image of each color on the corresponding photoconductive member. The image forming device develops the latent image into a toner image and transfers the toner image in a superposing manner to either the transfer sheet on the conveyor member or the intermediate transfer member.
The conveyor member and the intermediate transfer member are often shaped as a belt, but the shape thereof is not limited thereto.
A method in which the toner image is transferred directly onto the transfer sheet may be referred to as a direct transfer method. A method in which the toner image is first transferred onto the intermediate transfer member and then retransferred onto a transfer sheet may be referred to as an intermediate transfer method. Both the direct transfer method and the intermediate transfer method may be used.
Since the toner image of each color is formed on an individual photoconductive member, the toner images of respective color components after being transferred onto the transfer sheet or the intermediate transfer member may not be perfectly superposed on each other, thus creating color misregistration.
To correct the color misregistration, the background image forming apparatus may include a misregistration correction function to adjust a writing timing in the main scanning direction in a unit of a pixel width, which corresponds to a cycle of a pixel clock signal. The background image forming apparatus may further include a misregistration correction function to adjust a writing timing in the sub-scanning direction in a unit of a scan line width, which corresponds to a sub-scanning frequency.